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Subject[PATCH 09/15] readahead: add tracing event
Example output:

# echo 1 > /debug/tracing/events/readahead/enable
# cp test-file /dev/null
# cat /debug/tracing/trace # trimmed output
readahead-initial(dev=0:15, ino=100177, req=0+2, ra=0+4-2, async=0) = 4
readahead-subsequent(dev=0:15, ino=100177, req=2+2, ra=4+8-8, async=1) = 8
readahead-subsequent(dev=0:15, ino=100177, req=4+2, ra=12+16-16, async=1) = 16
readahead-subsequent(dev=0:15, ino=100177, req=12+2, ra=28+32-32, async=1) = 32
readahead-subsequent(dev=0:15, ino=100177, req=28+2, ra=60+60-60, async=1) = 24
readahead-subsequent(dev=0:15, ino=100177, req=60+2, ra=120+60-60, async=1) = 0
CC: Ingo Molnar <mingo@elte.hu>
CC: Jens Axboe <jens.axboe@oracle.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
include/trace/events/readahead.h | 78 +++++++++++++++++++++++++++++
mm/readahead.c | 11 ++++
2 files changed, 89 insertions(+)
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux/include/trace/events/readahead.h 2010-02-24 10:44:46.000000000 +0800
@@ -0,0 +1,78 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM readahead
+
+#if !defined(_TRACE_READAHEAD_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_READAHEAD_H
+
+#include <linux/tracepoint.h>
+
+#define show_pattern_name(val) \
+ __print_symbolic(val, \
+ { RA_PATTERN_INITIAL, "initial" }, \
+ { RA_PATTERN_SUBSEQUENT, "subsequent" }, \
+ { RA_PATTERN_CONTEXT, "context" }, \
+ { RA_PATTERN_THRASH, "thrash" }, \
+ { RA_PATTERN_MMAP_AROUND, "around" }, \
+ { RA_PATTERN_FADVISE, "fadvise" }, \
+ { RA_PATTERN_RANDOM, "random" }, \
+ { RA_PATTERN_ALL, "all" })
+
+/*
+ * Tracepoint for guest mode entry.
+ */
+TRACE_EVENT(readahead,
+ TP_PROTO(struct address_space *mapping,
+ pgoff_t offset,
+ unsigned long req_size,
+ unsigned int ra_flags,
+ pgoff_t start,
+ unsigned int size,
+ unsigned int async_size,
+ unsigned int actual),
+
+ TP_ARGS(mapping, offset, req_size,
+ ra_flags, start, size, async_size, actual),
+
+ TP_STRUCT__entry(
+ __field( dev_t, dev )
+ __field( ino_t, ino )
+ __field( pgoff_t, offset )
+ __field( unsigned long, req_size )
+ __field( unsigned int, pattern )
+ __field( pgoff_t, start )
+ __field( unsigned int, size )
+ __field( unsigned int, async_size )
+ __field( unsigned int, actual )
+ ),
+
+ TP_fast_assign(
+ __entry->dev = mapping->host->i_sb->s_dev;
+ __entry->ino = mapping->host->i_ino;
+ __entry->pattern = ra_pattern(ra_flags);
+ __entry->offset = offset;
+ __entry->req_size = req_size;
+ __entry->start = start;
+ __entry->size = size;
+ __entry->async_size = async_size;
+ __entry->actual = actual;
+ ),
+
+ TP_printk("readahead-%s(dev=%d:%d, ino=%lu, "
+ "req=%lu+%lu, ra=%lu+%d-%d, async=%d) = %d",
+ show_pattern_name(__entry->pattern),
+ MAJOR(__entry->dev),
+ MINOR(__entry->dev),
+ __entry->ino,
+ __entry->offset,
+ __entry->req_size,
+ __entry->start,
+ __entry->size,
+ __entry->async_size,
+ __entry->start > __entry->offset,
+ __entry->actual)
+);
+
+#endif /* _TRACE_READAHEAD_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
--- linux.orig/mm/readahead.c 2010-02-24 10:44:45.000000000 +0800
+++ linux/mm/readahead.c 2010-02-24 10:44:46.000000000 +0800
@@ -19,6 +19,9 @@
#include <linux/pagevec.h>
#include <linux/pagemap.h>

+#define CREATE_TRACE_POINTS
+#include <trace/events/readahead.h>
+
#define MIN_READAHEAD_PAGES DIV_ROUND_UP(VM_MIN_READAHEAD*1024, PAGE_CACHE_SIZE)

static int __initdata user_defined_readahead_size;
@@ -322,6 +325,11 @@ int force_page_cache_readahead(struct ad
offset += this_chunk;
nr_to_read -= this_chunk;
}
+
+ trace_readahead(mapping, offset, nr_to_read,
+ RA_PATTERN_FADVISE << READAHEAD_PATTERN_SHIFT,
+ offset, nr_to_read, 0, ret);
+
return ret;
}

@@ -349,6 +357,9 @@ unsigned long ra_submit(struct file_ra_s
actual = __do_page_cache_readahead(mapping, filp,
ra->start, ra->size, ra->async_size);

+ trace_readahead(mapping, offset, req_size, ra->ra_flags,
+ ra->start, ra->size, ra->async_size, actual);
+
return actual;
}




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